The invention relates to a method and a base station system for channel allocation in a radio communications system, in particular in a mobile radio system having broadband channels, in which signals are transmitted in accordance with a TD/CDMA subscriber separation method.
Mobile radio systems in which radio cells which use the same frequency band each have separate timeslots are described in EP 0 536 864 A and WO 97/12489. The timeslots are in this case split up both for the downlink direction and for the uplink direction.
In radio communications systems, information (for example voice, video information or other data) is transmitted using electromagnetic waves via a radio interface between a transmitting and a receiving radio station (base station and mobile station, respectively). The electromagnetic waves are in this case transmitted at carrier frequencies which are in the frequency band intended for the respective system. Frequencies in the frequency band around 2000 MHz have been provided for future mobile radio systems using CDMA or TD/CDMA transmission methods via the radio interface, for example the UMTS (Universal Mobile Telecommunication System) or other 3rd generation systems.
Frequency division multiplex (FDMA), time division multiplex (TDMA) or a method which is known as code division multiplex (CDMA) are used to distinguish between the signal sources, and thus for evaluation of the signals. A radio communications system using the TDMA transmission method is known from U.S. Pat. No. 5,719,859 A.
A radio communications system which combines these methods is known from DE 195 49 148 A1. In contrast, the GSM mobile radio system uses only a combination of FDMA and TDMA. Both systems use a frequency reuse cluster of considerably more than unity, so that the interference between adjacent base stations is reduced by the FDMA component. In systems such as these, channel allocation methods always relate exclusively to the FDMA component.
It is accordingly an object of the invention to provide a method and a base station system which overcomes the above-mentioned disadvantageous of the prior art apparatus and methods of this general type, and in which the interference is reduced even when the frequency reuse cluster tends to unity.
With the foregoing and other objects in view there is provided, in accordance with the invention a method for channel allocation in a radio communications system, which includes using a TDMA transmission method to carrying out radio transmission between mobile stations and base stations; allocating at least partially different timeslots to a first base station and to a second base station for transmissions in a downlink direction; and transmitting in an uplink direction without splitting the timeslots between the first base station and the second base station.
According to the invention, a first portion of the timeslots is allocated to a first base station and a second portion of the timeslots is allocated to a second base station. The interference between adjacent base stations is thus extremely reduced without the assistance of any FDMA component, that is to say, in the worst case, for a radio communications system having a frequency reuse cluster of unity. A fixed allocation to two base stations thus results in a time cluster of two. If further portions of the timeslots are allocated to further base stations, then a time cluster of three, four etc., can be produced.
In contrast to known radio communications systems, the resource xe2x80x9ctimeslotxe2x80x9d is split up within the system. This is advantageous in particular in broadband radio communications systems, in which only a small number of frequency bands are available, for example in the xe2x80x9cunpaired bandxe2x80x9d for the 3rd mobile radio generation. One advantageous application is a mobile radio system using a TDD transmission method (time division duplex) between mobile stations and base stations, in which timeslots in one frequency band are used for the uplink direction and downlink direction.
In accordance with an added feature of the invention, the allocation of the first and second portions of the timeslots is exclusive, so that the base stations transmit and receive only in the timeslots allocated to them. In this case, the interference between the base stations is considerably reduced.
A major advantage with regard to best-possible utilization of the radio resources is provided by a hybrid channel allocation method. In this case, the first and second portions of the timeslots are permanently allocated, and a third portion of the timeslots is allocated dynamically. The hybrid channel allocation method combines the advantages of the permanent and dynamic channel allocation concepts, in this context see I. Katzela and M. Naghshineh, xe2x80x9cChannel Assignment Schemes for Cellular Mobile Telecommunication Systems: A Comprehensive Surveyxe2x80x9d, IEEE Personal Communications, June 1996, pages 10-31. The partially permanent allocation keeps the signaling complexity low, and the partially dynamic allocation concentrates a high data rate onto individual cells. The latter is possible, in particular, if the third portion of the timeslots can be allocated to a plurality of base stations on a load-related basis. Thus, even high data rates, for example 384 kbps, can be allocated to an individual subscriber, since the radio resources are not excessively fragmented.
In accordance with an additional feature of the invention, the timeslots in the third portion are advantageously allocated locally, that is to say by the base station. It is also possible for individual timeslots to be used simultaneously by a plurality of base stations.
In accordance with an another feature of the invention, the mobile station is allocated a timeslot in the first portion with higher priority than a timeslot in the third portion. There is a thus a high probability of resources which can be allocated dynamically being available when needed. Furthermore, a timeslot in the third portion is allocated for the mobile station with higher priority than a handover to an adjacent base station.
To allow an adequate timeslot to be allocated for a radio connection, interference measurements are carried out by the base station and/or by the mobile station, so that a suitable timeslot is selected for a connection or, when a timeslot is released by another connection, a handover of the connection to this timeslot is initiated.
The time orthogonality of th e utilization of timeslots for different cells can be limited to the user information transmission. Advantageously, an organization channel is set up in the downlink direction, and/or an access channel for a plurality of base stations is set up in the uplink direction, in each case in a common timeslot. These measures improve resource utilization.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in method and base station system for channel allocation in a radio communications system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.